The present invention relates to a refrigeration apparatus including an evaporator which constitutes an annular refrigerant circuit together with a cooling unit constituted of a compressor, a radiator, a pressure reduction unit and the like and which is provided on a cooling target side.
Heretofore, in this type of refrigeration apparatus, a refrigerant cycle is constituted by successively annularly connecting a compressor (e.g., a rotary compressor), a radiator, a pressure reducing unit (an expansion valve, a capillary tube, etc.), an evaporator and the like via pipes. A refrigerant gas sucked into the compressor is compressed in this compressor to form a high-temperature high-pressure refrigerant gas, and the gas is discharged to the radiator. The refrigerant gas releases heat in this radiator, then the pressure of the gas is reduced by pressure reducing means, and the gas is supplied to the evaporator. The refrigerant evaporates in the evaporator, and absorbs the heat from a surrounding area at this time to exert a cooling function.
Here, in recent years, to cope with a global environment problem, an apparatus has been developed in which carbon dioxide as a natural refrigerant is used as the refrigerant even in this type of refrigerant cycle without using conventional Freon and in which a supercritical refrigerant cycle operated with a supercritical pressure on a high pressure side is used.
In such a supercritical refrigerant cycle apparatus, to prevent a liquid refrigerant from returning to the compressor and being compressed, an accumulator is arranged on a low pressure side between an outlet side of the evaporator and a suction side of the compressor, the liquid refrigerant is accumulated in this accumulator and the gas only is sucked into the compressor. Moreover, the pressure reducing unit is adjusted so that the liquid refrigerant in the accumulator does not return to the compressor (e.g., see Japanese Patent Publication No. 7-18602 (Patent Document 1)).
However, when the accumulator is provided on the low pressure side of the refrigerant cycle, more refrigerant needs to be introduced. Moreover, to prevent the liquid refrigerant from being fed back as described above, the capacity of the accumulator needs to be enlarged, or the diaphragm adjustment of the pressure reducing unit needs to be performed. In consequence, the enlargement of an installation space or the lowering of the refrigeration capability in the evaporator is incurred.
To solve the problem, heretofore, an internal heat exchanger has been disposed in which heat exchange is performed between the refrigerant discharged from the radiator and the refrigerant discharged from the evaporator. FIG. 8 shows a perspective view of a conventional internal heat exchanger 100. This internal heat exchanger 100 includes a high pressure side flow path 101 through which the refrigerant from the radiator flows, and a low pressure side flow path 102 through which the refrigerant from the evaporator flows. The refrigerant from the radiator flows into the high pressure side flow path 101 from a refrigerant inlet 101A provided on the downside of the internal heat exchanger 100, and is discharged from a refrigerant outlet 101B provided on the upside of the internal heat exchanger 100. The refrigerant from the evaporator flows into the low pressure side flow path 102 from a refrigerant inlet 102A provided on the upside of the internal heat exchanger 100, and is discharged from a refrigerant outlet 1028 provided on the downside of the internal heat exchanger 100.
In consequence, when the heat exchange between the refrigerant from the radiator and the refrigerant from the evaporator is performed, the temperature of the refrigerant entering the pressure reducing unit is lowered to enlarge an entropy difference between the evaporators, whereby the refrigeration capability is improved (e.g., see Japanese Patent Application Laid-Open No. 2005-226913 (Patent Document 2)).
However, in the above refrigerant cycle apparatus disclosed in Patent Document 2, the internal heat exchanger is constituted of a double pipe to prevent the liquid refrigerant from being fed back with low cost. However, to realize predetermined heat exchange, a long double pipe needs to be constituted, and a refrigerant flow rate needs to be secured. However, such an internal heat exchanger is installed together with the compressor and the radiator in a refrigerator-side unit, and hence the installation space of the internal heat exchanger is restricted. To solve the problem, the diameter of the pipe is decreased, and the pipe is bent a plurality of times, when formed. In consequence, the heat exchanger can be installed in a small space while securing a necessary refrigerant flow rate (length).
However, since the pipe diameter decreases, a sectional area decreases with respect to the predetermined refrigerant flow rate, and the refrigerant flow rate is accelerated. In consequence, the pressure loss of the refrigerant circulated through the apparatus increases, which results in a problem that the performance of the refrigeration apparatus is lowered.